Stackable armchair



FIG. 1 is a front perspective view of a stackable armchair, showing my design;

FIG. 2 is a front elevational view; and,

FIG. 3 is a side elevational view, the opposite side being a mirror image thereof.

The undisclosed rear surface of the chair is conventionally plain in appearance. 

The ornamental design for a stackable armchair, as shown and described. 